1. Field of the Invention
The present invention relates to a magnetic disk drive, and more particularly to a high-recording-density magnetic disk drive in which any change in the distance between the magnetic disk and the magnetic head is minimized and which is reduced in size and weight.
2. Description of the Related Art
Generally, in magnetic disk drives, a magnetic head is moved radially across a magnetic disk while the magnetic disk is rotating, for forming concentric recording tracks on the magnetic disk. The magnetic head is moved radially across the magnetic disk to reach and follow a desired recording track (a process known as tracking) by a linear actuator or a rotary actuator that is positioned radially outwardly of the magnetic disk.
As the recording density of magnetic disk drives increases, there is a demand for reducing the distance or spacing between the magnetic disk and the magnetic head. With the spacing reduced, however, the magnetic head tends to be unable to catch up with variations caused by oscillations of the motor which rotates the magnetic disk or undulations of the magnetic disk itself. When this happens, the magnetic head jumps off a desired recording track, with the result that spacing-induced fluctuations and output electric signals from the magnetic head are subject to large disturbances. Consequently, it has been difficult to increase recording density beyond a certain limit.
In order to reduce eccentricity of magnetic disks, it is necessary to increase the diameter of a bearing which supports the shaft of the motor. Therefore, it is difficult to reduce the inside diameter of the magnetic disk, and hence the size of the magnetic head.
Because the actuator for radially moving the magnetic head is positioned radially outwardly of the magnetic disk, the support spring or arm which supports the magnetic head must be made large or long and undergoes large inertial forces. The large inertial forces pose a large burden on the servo control system, making it difficult to effect high-speed tracking.
As a result, the conventional magnetic head drives have not been easy to reduce in size.